This invention relates generally to circuit board assemblies and, more particularly, to a method and apparatus for mounting an electrical module on a circuit board.
A byproduct of normal operation of an electrical circuit is thermal energy, i.e., heat. Thermal energy is generated as a result of frictional effects of charge flow during operation of the electrical circuit. Greater charge flows, i.e., larger currents, generate a greater buildup of thermal energy. If not properly dissipated, a buildup of thermal energy can cause undesirable operating characteristics in the electrical circuit, and can even cause damage to the components of the electrical circuit, as well as components of other proximate circuits.
Generation of thermal energy is particularly significant in amplification devices such as, for example, a power amplifier. Because power amplifiers often amplify the input signals supplied thereto, signals output by the power amplifier can be many times the amplitude of the input signals. However, the efficiency of a typical power amplifier is only about 40% and therefore, about 60% of the input electrical energy supplied to these amplifiers is converted into thermal energy. In order to prevent damage from occurring to the power amplifier (as well as to other proximately positioned components), it is necessary to dissipate this thermal energy by thermally coupling the power amplifier to a heat sinking element. Due to the large amount of thermal energy generated by the operation of these power amplifiers, heat dissipation can be readily accomplished by using the metal housing, which contains the substrate on which the power amplifier is mounted, as a heat sinking element. By creating a thermally conductive path between the power amplifier and the metal housing, thermal energy contained in, or generated during the operation of, the power amplifier can be conducted to the metal housing and dissipated by convection.
It is known to mount a power amplifier such that its thermal energy is conducted to the metal housing. For example, the power amplifier is mounted on, and electrically connected via solder to, a metal plate attached to a circuit board that physically contacts the metal housing. Therefore, a thermally conductive path of power amplifier-solder-metal plate-chassis is realized. Unfortunately, the presence of the metal plate, which is sandwiched between the power amplifier and the circuit board, degrades heat transfer between the power amplifier and metal housing.
An additional mounting difficulty of known power amplifier assemblies occurs during automated electrical circuit assembly. The power amplifier must be removed from the automated process to undergo a separate "manual" mounting sub-process. For example, it is known to manually attach a metal plate to the circuit board and hand solder the power amplifier onto the top of the metal plate while the leads of the power amplifier are also hand soldered to corresponding pads on the circuit board. Only after the completion of this manual sub-process can the circuit board with the power amplifier be re-injected into the automated assembly process. The requirement of a separate assembly sub-process significantly increases production costs.
Therefore, a need exists for an improved method and apparatus for mounting an electrical module on a circuit board which facilitates automated circuit assembly.